Highly halogenated organic chemicals are favored in industry due to their many useful properties, such as stability under heat and pressure. However, these chemicals are sometimes toxic to flora and fauna. Improper disposal or spills of these organic chemicals may contaminate the environment. Cleanup is necessary due to the considerable health hazard and environmental stability of these chemicals.
In the past, an acceptable procedure for cleaning up a contaminated area involved removal of the contaminated soil or material to a designated secure landfill. Due to recent and upcoming federal regulations, the types and amounts of organic materials that can be disposed of in such a designated landfill have been greatly reduced. Therefore, there is a growing need to sanitize soils with an efficient and economical treatment process.
At present, the only generally accepted treatment technology for destroying highly halogenated organic contaminants is incineration. Application of incineration to soil treatment is inefficient because the contaminants to be incinerated are adhered to a large mass of inert material. In treating soil, incineration would involve collecting, packaging and transporting a large mass of contaminated material to a licensed incineration facility, heating the large mass of inert solids to very high incineration temperatures to decompose the proportionately small amount of target contaminants, and packaging and returning the materials back to the treatment site from where they were removed, or disposed of in a secure landfill.
In addition to the labor cost, the transportation cost, and the energy cost there is also a problem in that the capacity of present licensed incineration facilities is currently limited. Further, during incineration some of the halogenated contaminants may be converted to dioxin which is approximately 10,000 times as carcinogenic as an equal amount of PCB; thus special precautions must be implemented to prevent release into the atmosphere of this highly toxic by-product.
A similar process to incineration for the disposal or cleanup of contaminated wastes is pyrolysis. Such a process is disclosed in U.S. Pat. No. 4,301,750 (Fio Rito et al.), where waste materials, such as wood waste from lumber mills, are pyrolyzed in a rotating dryer. This pyrolysis process is operated at temperatures on the order of 3,000.degree. to 4,000.degree. F.
As an alternative to incineration and pyrolysis, chemical processes have been developed for decontamination of contaminated soil, which basically involve treatment with a desorbent and dehalogenating agent. An example of such a chemical treatment is provided in U.S. Pat. No. 4,574,013 (Peterson). A typical reaction scheme involves concurrently reacting an alkali metal hydroxide with an alcohol to form an alkoxide and water; reacting the alkoxide with the unwanted halogenated aromatic contaminant to form an ether and a salt; permitting the ether to decompose to a phenol; and reacting the phenol with an alkoxide to form a water soluble phenate.
In such a chemical process the presence of water interferes with the chemical reaction scheme, thus the contaminated soil is preferably preliminarily dried to remove water. Drying involves removal of water, leaving dry contaminated soil. After the water has been removed, the soil is treated with the reagent and the chemical reaction is carried out in a basically sealed system. To accelerate the reaction, the contaminated soil may be mixed with the reagent in a cement mixer or similar device, with optional increase in temperature and pressure.
Similarly, U.S. Pat. No. 4,327,027 (Howard) discloses dehalogenation of halogenated aromatic compounds including PCB using anhydrous alkali metal salts of alcohols, preferably polyhydroxy alcohols. This reaction is also preferably carried out in an absence of moisture in a closed system.
Another dehalogenation technique is exemplified by U.S. Pat. No. 4,144,152 (Kitchens). Halogenated compounds, particularly PCB, are dehalogenated by photodegradation with UV radiation. The treatment method may be adapted to decontamination of soil by first washing the soil with a UV transparent carrier, such as an organic solvent, preferably methanol rendered alkaline by the addition of an alkali metal oxide or hydroxide, and then irradiating the UV transparent carrier containing the contaminant.
However, in the case where relatively small amounts of contaminants are adsorbed to large amounts of inert materials such as soil or sludge, each of the above techniques involves considerable expense and inconvenience. Transportation and energy costs are involved in conveying soil to an incineration facility and heating the large mass to incineration temperatures. The chemical treatment techniques are slow and may take weeks if not accelerated by increasing pressure or temperature, and involve the expense of start-up and expended chemicals for treating soil to desorb and dehalogenate contaminants.
Accordingly, a keen need has been felt for a more efficient, economical system and apparatus for separating contaminants from contaminated soil, sludge and other inert materials. There is also a need for a system that is adaptable to being transportable to a contaminated area.